Mooring Fatigue Assessment Evaluating Chain Twist and Out-of-Plane Bending for a Semi-submersible

A mooring fatigue assessment for mooring chain links of a semi-submersible in Offshore West Africa (OWA) is presented. Three cases that mooring chain links are subjected to pure tension, out-of-plane bending (OPB), and torque are considered in the assessment. For the case that mooring chain links are subjected to pure tension, a comparative study on S–N curves, T–N curves, and fracture mechanics (FM)-based mooring system fatigue analyses is made, and the results show that the fatigue lives predicted by these three approaches are generally comparable if the safety factors suggested by API and DNVGL are applied to T–N curves and S–N curves based approaches. For the cases that mooring chain links are subjected to the OPB and torque, the investigation shows that fatigue lives of mooring chain links are decreased significantly due to the OPB effects, while the decline of fatigue lives of mooring chain links happens when the twist angles are more than 10 deg.

A COMPARISON OF TESTING METHODS FOR DETERMINATION OF SPRAYED CONCRETE TENSILE STRENGTH

Sprayed concrete is important construction material in tunnelling. Primary lining is essential in NATM where the sprayed concrete can be loaded by tension due to bending moments. The tension is common reason of failure because concrete has a relatively low tensile strength. The tensile strength is usually determined by splitting tensile test in laboratory. However, the results can be distorted because the specimen is not loaded by pure tension in this case. The paper compares results of concrete tensile strength determined by two methods: indirect by the splitting tensile test and direct by the modified tensile test.

Silica-Based Infiltrations for Enhanced Zirconia-Resin Interface Toughness

Novel silica-based infiltrations on the surface of zirconia have the potential to improve their bondability, allowing for the etching/silane adhesive bonding technique. Nonetheless, adhesively bonded joints are subject to mixed tensile and shear stresses when the restoration is in occlusal service. Thus, we aimed to investigate the effect of 2 novel silica-based infiltrations on the interfacial toughness of adhesively bonded zirconia using the Brazil nut method, which allows for controlled types of stresses to be applied at the interfaces. In total, 150 3Y-TZP (In-Ceram YZ; Vita) Brazil nuts were machined and randomly assigned to 3 groups: C, control (air abraded); SG, sol-gel silica infiltration; and GI, glass infiltration. SG specimens were immersed twice in silicic acid for 20 min and dried (100°C, 1 h). GI specimens were presintered (1,400°C, 1 h) before a glass powder slurry was applied to the intaglio surface. All specimens were then sintered (1,530°C, 2 h). Following adhesive bonding (Panavia F 2.0, Kuraray) and water storage (37°C) for 10 d, the Brazil nuts were subdivided into groups baseline and aged (40,000 thermal cycles between 5°C and 55°C, with a dwell time of 30 s). The Brazil nuts were subjected to axial-loading tests using various inclinations (precrack angle with load direction): Θ = 0°, 5°, 10°, 15°, or 25°, which define the stress type at the interface, from pure tension (0°) to increasing levels of shear. Under pure tension (0°), GI yielded superior interfacial fracture energy, SG and C were similar, and aging had no effect. Under predominantly shear stresses (25°), aging significantly decreased interfacial fracture energy of C and SG, while GI remained stable and was superior. The glass infiltration of the zirconia intaglio surface increases its adhesive bonding interfacial toughness. The sol-gel silica infiltration method requires improvement to obtain a homogeneous surface infiltration and an enhanced bond strength.

Pure-tension non-linear sliding mode control for deployment of tethered satellite system

This paper presents a sliding mode controller for the deployment of two-body tethered satellite system. A sliding surface design for underactuated system is employed to reconcile pure-tension control scheme with non-linear coupled deployment dynamics. The proposed sliding surface is strictly non-linear. Hence, the control scheme does not require linearization operation of tethered satellite system and can guarantee that all the system states converge to zero with arbitrary small errors. To deal with input constraint of pure-tension control, an adaption is introduced into the controller design to remove the negative effect caused by input constraint in stability analyses and ensures the feasibility of the proposed controller even though command input overtakes the tolerance of tension actuator. To avoid the chattering phenomena, the trivial sign function is removed from the switching input and replaced by the disturbance observer. Numerical results demonstrate the effectiveness of the proposed controller for the deployment of the tethered satellite system.